Engines operating with a variable number of active or deactivated cylinders may be used to increase fuel economy, while optionally maintaining the overall exhaust mixture air-fuel ratio about stoichiometry. In some examples, half of an engine's cylinders may be disabled during selected conditions, where the selected conditions can be defined by parameters such as a speed/load window, as well as various other operating conditions including vehicle speed. A VDE control system may disable selected cylinders through the control of a plurality of cylinder valve deactivators that affect the operation of the cylinder's intake and exhaust valves. Methods for monitoring valve operation in cylinders may be used to diagnose proper switching between VDE and non-VDE modes to ensure a proper transition.
One example approach for monitoring valve operation in cylinders is shown by Takao et al. in JP 2006226266. In this example, the output of a valve position sensor is used in combination with the output of an air/fuel ratio (AFR) sensor to identify aberrant exhaust valve function. Specifically, if the position sensor detects a distance from a reference position greater than a predetermined threshold, over a plurality of engine cycles, in addition to the AFR sensor detecting a change in the air/fuel ratio, degradation in the operation of a cylinder exhaust valve is concluded.
However, the inventors herein have recognized several potential issues with such an approach. As one example, the method assumes a higher occurrence of an imperfect exhaust valve closing as compared to an imperfect intake valve closing, thereby making the system insensitive to degradation in intake valve operation. For example, in the event of intake valve degradation with no significant change in AFR, the method may not detect any valve degradation. In another example, in an engine operating with a variable valve lift mechanism, the method may not be able to distinguish between valve lift profiles such as a high lift and a low lift profile. Further still, the method may not properly detect transient and/or single cycle valve faults.
Thus, in one example, the above issues may be addressed by a method of monitoring cylinder valve deactivation in an engine operating with a plurality of cylinder valves, the method comprising, sensing a plurality of cylinder valve positions of a plurality of cylinder valves and combining the plurality of sensed positions to form a combined cylinder valve signal. In this way, it is possible to utilize a plurality of sensed valve positions to identify either or both of intake or exhaust degradation, without requiring individual monitoring of each sensor. Further, individual valve degradation, such as degradation in VDE valve transitions, can also be identified based on the combined signal, and further based on a crank angle at which the combined signal differs from an expected value.
In one particular example, the engine is a four-cylinder variable displacement engine with two valves per cylinder, the operation of each valve monitored by respective rocker arm position sensors coupled to respective valve rocker arms. Herein, the sensor signals for all the intake valves, and likewise all the exhaust valves, may be coupled together electrically to generate combined cylinder valve signals such that the behavior of the 8 valves may be indicated by only two electrical inputs to a control system. In another example where the four cylinders are divided between two banks, the sensor signals for bank-specific intake and exhaust valves may be combined together.
In either sensing configuration, the sensor signals may be coupled together electrically such that changes in valve lift to any of the coupled valves affects the generated output. When sensing the plurality of valve positions, a respective binary value may be formed for each of the sensed positions. The plurality of sensed positions may be combined to form a combined cylinder valve signal. Herein, the binary values may be combined to form a binary combined valve signal value. The combined signal may be sampled in each of a plurality of sampling windows, such as a crank angle sampling window. An expected value of the combined cylinder valve signal may be calculated by a control system based on a VDE mode of operation. If the combined cylinder valve indication signal is an unexpected signal, a control system may indicate valve degradation and further identify the degraded valve between the plurality of valves sensed based on the crank angle sampling window at which the expected value differs from the combined signal.
In this way, the number of valve position inputs received and processed by a control system may be reduced without affecting the control system's ability to discern individual valve faults. In a variable displacement engine operating with a plurality of cylinder valves, the method may be used to monitor proper switching between VDE and non-VDE modes of operation. As such, the method also enables detection of single cycle valve faults which, if left unchecked, can contribute to degradation of valve train components such as deactivating pins and pistons, valves and valve seats. Thus, by enabling the detection of single cycle faults, fatigue failure of valve train components can be averted. By allowing a faster detection of degraded valve operation, adverse impacts thereof on engine fuel efficiency and performance can be reduced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.